1. Field of the Invention
The present invention relates to a downhole tool for enhancing the force of a downhole jarring tool. More particularly, the present invention relates to a downhole tool capable of enhancing an upward jarring blow or a downward jarring blow emanated from a double acting hydraulic well jar useful in coiled tubing and conventional drilling applications.
2. Description of the Related Art
Jarring tools are used to free stuck drill pipe or well tools in a well bore. They provide a substantial upward or downward jarring action in an effort to transmit sufficient force to dislodge a stuck member. Double acting jars which can transmit either upward or downward jarring loads are well known in the prior art. See, for example, U.S. Pat. Nos. 4,186,807; 4,865,125; and 5,007,479. Such jars typically use a hydraulic-type fluid to isolate well bore pressure and provide the working fluid through which the jarring tool operates.
It may also be helpful to employ a downhole tool proximate the jarring tool which serves to enhance or accentuate the force exerted by the jarring tool on the stuck tool in either the upward jarring mode or the downward jarring mode. Typically, such tools serve to accelerate the rate at which the hammer of a jarring tool strikes the anvil or other portion which generates the jarring action. Examples of enhancers or accelerators are set forth in U.S. Pat. Nos. 3,735,828; 4,846,237; 5,232,060; 5,425,430; and 5,584,353.
With the advent of coiled tubing techniques, the need exists for a variety of downhole tools capable of performing their traditional functions but in the confines of a coiled tubing application. Briefly, a coiled tubing operation involves the use of a single continuous pipe or tubing for drilling or workover applications rather than the more traditional 30-foot drill pipe sections. The tubing, which is coiled onto a reel and uncoiled as it is lowered into the well bore, can be used for either drilling or workover applications. However, coiled tubing presents a number of working constraints to existing tool design. First, due to the size of the coiled tubing, limited compressive and tensile loads can be placed on the tubing by the rig operator. Essentially, this means that downhole tools which require tensile or compressive force to operate, such as a jarring tool, must be capable of operating with the limited compressive load capability of coiled tubing. In addition, in coiled tubing application the overall length of the downhole tool becomes significant since there is limited distance available between the stuffing box and the blowout preventor to accommodate the bottom hole assembly. A typical bottom hole assembly includes a quick disconnect, an enhancer or accelerating tool, a sinker bar located below the enhancer to provide weight to the bottom hole assembly, the jarring tool, a release tool below that of some type, and then an overshot. There may be other tools as well which may be needed. Thus, the length of the jarring tool enhancer becomes particularly significant since the entire bottom hole assembly must fit within the limited distance between the riser and blowout preventor to introduce it into a pressurized well. Furthermore, within these confines, the jarring tool enhancer must have a large enough internal bore to permit pump-down tools to pass. Thus, the coiled tubing jarring tool enhancer must have a limited overall wall thickness in view of limited outer diameter conditions, and must be of limited length.
As in the case of traditional drill pipe, coiled tubing or other down hole tools may get stuck in the well bore at times. Under these circumstances, the ability to generate an enhanced load through a mechanism which accelerates the jarring motion of the jarring tool and introduces an auxiliary force is particularly advantageous. Thus, the need exists for a jarring tool enhancer which can satisfy the limited load, limited length, and large bore requirements of coiled tubing application as mentioned above. Preferably, such a jarring tool enhancer would have application in a conventional drill string as well.